ORNL Uses New 3-D Printers To Break Down Development Barriers

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Additive manufacturing has captured industry's imagination, but even as the first parts appear inside jet engines, the technology's possibilities are only just being realized. As researchers experiment with new materials and optimized designs made possible by 3-D printing, the potential scale of the revolution in manufacturing is becoming clearer.

EADS Innovation Works and EOS, a leader in direct metal laser-sintering, have shown that replacing a cast-steel nacelle hinge bracket on an AirbusA320 with an additively manufactured titanium part, optimized to place metal where there are loads (see photos), cuts raw-material consumption 75%, saves 10 kg per shipset and reduces energy and emissions in production, operation and end-of-life recycling.

The challenge is to think beyond current materials and designs. To that end, Oak Ridge National Laboratory (ORNL) in Tennessee is placing thousands of 3-D printers in U.S. schools to give future designers and engineers experience with the technology. Already the lab has helped local high schools in the First Robotics competition—including building the first all-additive robot. Beginning this year with 250 machines, the lab plans to place 3,000 printers next year, then 4,000 and finally 28,000 so every high school in First Robotics has one.

Available desktop 3-D printers are being tested at ORNL to assess their capabilities. The lab's goal is to move from prototyping to production and enable distributed, “democratized” manufacturing where 3-D printers are a source of revenue for everybody, says Lonnie Love, group leader for automation, robotics and manufacturing—a high-tech return to the cottage industries that predated the Industrial Revolution.

Looking beyond consumer machines, ORNL is pushing the capabilities of additive manufacturing in the materials, complexity and scale of components that can be printed. The lab is completing perhaps the most complex all-additive design yet: a two-armed, neutrally buoyant underwater robot for the Office of Naval Research. Channels for hydraulics and wiring, cylinders and cams for pistons actuating the joints are all integrated inside the printed metal arms. There are no external pipes or wires. “We are pushing the envelope in additive manufacturing and robotics with this,” says Love.

ORNL, meanwhile, is working with additive-manufacturing equipment suppliers such as Arcam to expand the technology to new metals and larger parts, including laser-sintering of Inconel 718, a high-temperature superalloy used in turbine blades. But some of the most exciting work involves printing of reinforced plastics. Current 3-D-printed polymer parts are low-strength, and can be used for ducting but not load-carrying components. Now the lab has developed a way to infuse reinforcing carbon fibers into the raw material to print parts that can carry loads.

At 5-7 micrometers, conventional chopped carbon fibers are too thick to squeeze into the 0.25-in.-dia. thermoplastic filament that is fed into fusion-deposition molding (FDM) machines. ORNL has developed a way of producing fibers less than 500 nanometers in diameter.

When chopped, these nanofibers are small enough to mix into the FDM raw material, but have a length-to-diameter ratio high enough to achieve the reinforcing effect. Strengths on par with 6000-series aluminum are possible, says Chad Duty, group leader for deposition science and technology.

Infusing reinforcing fibers into raw material is a key to scaling up 3-D printing to large parts—60-100 ft. in size—for aerospace. ORNL calls this broad-area additive manufacturing, and the lab has been working with Lockheed Martin and an equipment manufacturer to develop the capability, initially to produce low-cost tooling but ultimately to print structures such as the wings of a large unmanned aircraft.

Large printed parts can warp because areas with different thicknesses cool at different rates—a core technical challenge with additive manufacturing. Adding 13% by volume of chopped carbon fiber to the thermoplastic-pellet feedstock provides twice the strength and four times the stiffness, and stops parts-warping as they cool, says Love.

As a next step, ORNL is working with an equipment supplier to build the prototype of a single machine that will print plastic parts, machine them to final shape and wrap them in re-inforcing carbon-fiber tows to produce large structural components.

“We work with the equipment makers, because the OEMs want this technology throughout their supply base,” says Craig Blue, director of ORNL's advanced manufacturing program.